The Environmental Changes Based On Stalagmite Records During Middle-Late Holocene And Carbon Isotope Monitoring Research Of A Karst Cave In Western Henan,China

In today’s world, global warming and frequent extreme weather events cause great threat on human living environment and survival is not only just a discipline problem but also today’s most important social issues of concern in human society. The study of past climate changes is an important method for understanding the Earth’s climate system changes and current climate changes, and it is also a good way to predict future climate changes. Meanwhile, we should strengthen the modern monitoring and simulating mechanism of various geological records, as well as study of driving mechanism of climate change because it will also help us better understand the evolution of the Earth’s history and predict future climate changes to contribute to the harmonious and sustainable development of human society. Holocene is closely related to human evolution and human civilization, thus strengthening the study of paleoclimate during this period is essential. Study of various geological records show that climate changes are not stable within Holocene, and there are many fluctuations. Owing to some characteristics such as wide distribution, less interference and abundant proxies, stalagmite has gradually attracted the attention of scholars. However, in recent years the researchers pay more attention to the stalagmites oxygen isotopes, and there have been many disputes because the controlled factors of stalagmite carbon isotope are more complex,, therefore we must be more comprehensive, and do more in-depth interpretations and argumentation on the forming mechanism of carbon isotopes of speleothems through cave monitoring and regional studies.This paper studies DSY1 stalagmite of Dongshiya cave as the basic object in Luanchuan county, west of Henan provinces of northern China where has less study of speleothems records, and we preliminary discuss the climate evolution of this region in middle-late Holocene by stalagmite carbon and oxygen isotope records. In order to better understand carbon isotope migration law of Karst caves, as well as for better interpretation of forming mechanism of speleothems, we select Jiguan cave as research and monitoring base nearby Dongshiya cave. We operated a dynamic monitoring of four complete hydrological years of the δ13CDIC of cave water as the main monitoring index and the analysis of δ13C of modern cave sedimentary from October 2009 to December 2013. Combining with the analysis of cave monitoring process of Jiguan cave and meteorological data, the preliminary discussion is about the response process to extreme climate events of carbon isotope of Krast cave which lies in the sensitive transitional south-north intersection in China of subtropical area to warm temperate zone in Asian monsoon areas. The results show that:(1) With 731 carbon and oxygen isotope data we obtained from Stalagmite DSY1,west of Henan we reconstructed the history of climate change in the middle-late Holocene of our study area and found that it has good reflection to “8.2ka BP event”, and “4.2ka BP event” within Holocene. But the carbon and oxygen isotopes of stalagmite DSY1 assumed inconsistent changing trends in the middle-late Holocene, the variation of δ18O is similar to stalagmite records of southern China, and it began positive around 6000 a BP, reflecting the trend of weakening of monsoon. It shows that the variations of oxygen isotope in western Henan province in middle-late Holocene have the same response mechanism with the oxygen isotopes of cave stalagmites of southern China in millennial scale, mainly reflecting changes in the transmission of ocean water vapor source; While the variation of δ13C began positive about 5000 a BP, and it is consistent with the most warm and humid period of Holocene climate, which is reflected by a variety of geological records in north of China. It is shown that the formation mechanism of stalagmite carbon isotope is complex, and we need an in-depth discussion combining past climate change with response of modern process.(2) the δ13CDIC of drip water(LYXS) ranges from-6.6 to 16.0‰,and the average is-11.8‰. The δ13CDIC value of two pool water(YZT, YCG) showed obvious seasonal cycle change: summer is lighter while winter is heavier. The value of cave water δ13CDIC responses to the conversion process of the El Ni?o and La Ni?a event from October 2009 to October 2010, during which period, the δ13CDIC of drip water is the lightest, while, the heaviest value appeared in June 2013. According to meteorological statistics, Luanchuan County suffered the worst drought during this period. Researching into the sensitive response of carbon isotope in Krast system to extreme climate events further confirmed that carbon isotopes of the cave sediments can be used as an effective tool to reflect climate change under appropriate conditions.(3) We discussed the periodic variation of carbon isotopes through the power spectrum analysis of the δ13C of stalagmite DSY1 in Dongshiya cave, west of Henan province, and found that there are 31a、32a、35a、38a、40a and 56 a cycles in carbon isotope, and these cycles are almost consistent with historical records of drought and flood. It shows precipitation within short scale is the main factors influencing the formation of stalagmite carbon isotopes. Combined the study of the response with process of modern cave monitoring, the impact of ENSO events should be taken into consideration in the reconstruction of high-resolution stalagmite carbon isotopic records. Matlab analysis of long scale record shows that there are a series of duration in 1500±600a heating and cooling cycles in stalagmite carbon isotope record of Dongshiya cave during the Holocene in the monsoon region. In addition to the solar radiation, the north Atlantic climate change may also affect the variation of the mid and low latitude monsoon in the Holocene.